DT News - MEA - Celtra Press — the most stable high-strength glass ceramic, regardless of testing method

Dentsply Sirona – Middle East

Mon. 1 June 2020

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Zirconia-reinforced lithium silicate (ZLS) has been available from Dentsply Sirona under the name of Celtra Press. With its three-point bending strength of more than 500 MPa, it has once again significantly raised the benchmark for high-strength glass ceramics.

Experiments conducted by the University of Giessen, Germany have now shown that Celtra Press is clearly ahead of its competitors also in terms of biaxial strength.

Internal measurements in a study of three-point bending strength have shown an average result of 567 MPa for Celtra Press.1 In comparison, the millable Celtra Duo ZLS (also from Dentsply Sirona) comes in at 210 unit bridges with up to the second premolar as distalmost abutment.

In addition to its superior three-point flexural strength, Celtra Press also exhibits the highest biaxial flexural strength among the high-strength glass ceramics, as researchers at the University of Giessen determined in recent laboratory experiments.2 The measured values were 678 MPa (Celtra Press), 413 MPa (Celtra Duo after finishing and polishing), and 560 MPa (Celtra Duo after glaze firing) (Fig. 1, Table 1).

Understanding strength measurements

Product literature and technical publications sometimes highlight a material’s three-point bending strength and sometimes its biaxial flexural axial test method are usually higher than those obtained by three-point bending test. The reason for that is that less effort is generally required to break the standard bar resting on two supports than the standard disk with three supports (Figs. 2 and 3).3 This is only partially compensated for by recalculation based on geometry data. In addition, the quality of the edge preparation in the biaxial samples is less important compared to the three-point supports.

The exceptionally high strength of Celtra Press is ensured by the addition of 10% of zirconia, which is completely dissolved in the glass matrix, and by a power firing step that is already integrated into the stain-and-glaze firing for monolithic restorations. But there is still another advantage of Celtra that will be immediately convincing to dentists: The material’s excellent surface properties permit intraoral polishing including, where required, finer occlusal adjustments—no separate glaze firing is required.

Table 1: Both the three-point bending test and the biaxial testing method result in Celtra Press being top-of-the-class among its competitors.

Fig 1: A new benchmark for the strength of high-strength glass ceramics: three-point and biaxial flexural strengths compared.

Fig. 2: In the three-point bending test, a bar resting on two supports is loaded from above with a punch until it breaks.

Fig. 3: The biaxial testing method loads a disk on three supports. The results of this test are generally higher than those of the three-point bending test.

References

In-house measurements by Dentsply Sirona.

Measurements carried out by the Department of Dentistry, Clinic for Dental Prosthetics, Justus Liebig University, Giessen, Germany

Yongxiang Xu, Jianmin Han, Hong Lin, Linan An. Comparative study of flexural strength test methods on CAD/CAM Y-TZP. Regen Biomater. 2015 Dec; 2(4): 239–244

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